1. Technical Field
The invention relates to data storage devices. More particularly, the invention relates to solid state data storage devices.
2. Description of the Prior Art
Floppy disk drives have slow access, low storage, and primitive data transfer rates, with no capability for fast data interaction on today's 16 and 32 bit computer systems.
For many years, the 5.25 inch floppy disk drive has been a dinosaur in the high technology, fast-moving data processing field.
5.25" Winchester disk drives have been heralded as the only new high capacity, high data transfer rate input/output (I/O) device for the personal computer. It took years even with high technology, for aggressive companies to optimize and miniaturize the components necessary for Winchester disk drives for low cost, small size, and high capacity requirements. Large bobbin servo linear positioning motors weighing 50 lbs. with dimensions of 12 inches by 8 inches have been replaced by the present 3 inch by 1.5 inch units weighing 0.5 lb. Stepper motors having 2 phases with 18 degree increments have given way to the present 5 phase motors with 0.72 degree step increments with micro-step, ramp-up, and ramp-down capabilities. Thus, present Winchester disk drives allow a microcomputer to control the absolute position of the read/write (R/W) heads in a manner similar to the closed loop servo actuated systems.
Past spindle drive systems utilized large cumbersome motors using belt-driven spindles. The insurgence of numerous drive manufacturers to miniaturize this large cumbersome device eventually brought about the creation of a "pancake style" spindle motor which uses multi-layered printed circuit board technology.
A present pancake style motor with a thickness of 0.25 inches can now generate the torque needed to spin the plated media used for the storage in a Winchester drive. The I/O controllers for the hard disk drives of yesterday were customized boards 48 inches by 48 inches with data transfer rates of 500 kbits/sec. These complex, bulky boards required extensive interconnection cabling and sensitive boot software to set-up on-board logic to perform the required data interaction between the host system and the hard disk drive. There are now many standard Winchester controllers of small size incorporating various advanced data retrieval systems. Modern devices typically have dimensions of 5.25 inches by 6 inches and are easily adaptable to many of the personal computers on the market with the added feature of a data transfer rate in excess of 5 Mbits/sec. Software was created to run the high tech drives that interface to the 16/32 bit micro-systems, and many thousands of hours were spent across the nation to accomplish this task.
The media and heads are the key and essential ingredients for the continued success of the 5.25 inch Winchester market. Equipment previously used for making integrated circuits began being used for making cobalt-coated 600 oersted 0.75 inch aluminum substrates for the demanding appetite of the 5.25 inch Winchester market. Unfortunately, this type of media is very expensive to produce. It has high material costs and low yields, and requires expensive manufacturing equipment. Further, the R/W heads are even more difficult to produce in adequate volumes and low costs.
2.00/3.50 inch floppy disk cartridge drives were next to appear on the market. With its small size, plastic molded parts, and a metal hub ring that allows the medium to be rotated at a 360/600 rpm speed, this cartridge had the effect of taking the flexible tape diskette from a primarily back-up storage device of slow speed to a medium capacity data storage device with slow data transfer rates. Thus, the 2.00 inch/3.50 inch floppy disk cartridge has solved none of today's needs for a small size storage tape backup device for the 5.25 inch Winchester disk drive (with storage capabilities now approaching 600 Million bytes in a 5.25 inch package).
In the art at the time of the writing of this application, a wide trade-off exists. A fixed media such as a Winchester disk has a very high storage capacity and relatively high access speed. However, in using a Winchester disk, if there is a problem with the storage media (the disk itself) it must be professionally replaced. Moreover, since the storage capacity is unexpandable, the total storage capacity of a fixed drive system such as a Winchester disk is equal to the amount of total storage on the single Winchester drive itself.
In contrast, solid state ferroelectric integrated circuit non-volatile memory, herein referred to as ferroelectric Random Access Memory or "FRAM" memory, has a relatively small storage capacity, no special requirements and no access time. "FRAM" is a registered trademark of RAMTRON Corporation of Colorado Springs, Colo.
Moreover, removable ferroelectric non-volatile memory packs--a pack having multi-layers of the same type board and a board consisting of many FRAM units on a single printed circuit board--may be interchanged, thus allowing the user to compile a library of packs. By buying a single drive and a plurality of packs, the user can thereby obtain many times the storage amount as found on a single Winchester drive by accumulating many removable solid state memory FRAM packs.
Prior art techniques for replacing rotating memory systems with solid state memory have been used for purposes other than using non-volatile solid state memory utilizing recording techniques for transferring data to rotating memory storage. For example, U.S. Pat. No. 4,298,956, granted May 14, 1979 discloses a digital read recovery with variable frequency using read only memory (ROM) integrated circuits. Another example is, U.S. Pat. No. 3,573,762, granted Apr. 6, 1971 which discloses a nonvolatile storage device used to replace disk drives using volatile READ/WRITE storage devices and non-volatile memory for control functions.
A trade off in designing disks also occurs. In a hard disk, the read/write head typically does not touch the disk, but rather "flies" over the surface of the disk, as close as possible to it. The condition of the head touching the disk is referred to as a head "crash" and causes catastrophic loss of the data encoded thereupon. Typically, as the height of the head over the disk decreases, the storage capacity and access speed can increase. However, once a certain small height occurs, the smoothness of the surface of the disk attains critical importance.
In contrast with the existing drive technology, the foundation of yesterday's memory used in the first computers were iron core memories. Core memories were long forgotten as slow, large, expensive, and power hungry memory devices. A major breakthrough was made that allows one to take advantage of the first core memories' non-volatile characteristics and also reduce their size a million fold.
Even though the theory of ferroelectrics was discovered in 1921, few attempts have been made to use this technology, and the first integrated circuits of small memory storage are just beginning to appear. Ferroelectric materials exhibit the same general characteristics of superconductor materials now in development.
Ferroelectric materials with non-volatile Q-V hysteresis loop characteristics similar to B-H loops in Iron magnetics will take the place of the rotating memory disk. There have been many prior art attempts to maximize the access rate and storage capacity of a disk. Typically, these involve improvements to the heads, controller circuitry and disk composition. It is an object of the present invention to provide improvements in all of the above-mentioned areas, and to produce a system that out-performs the state of the art as it now exists by a very large amount.